The Family Outcomes Survey–Revised (FOS-R) measures family outcomes of services for young children with disabilities or developmental delays, and it can be used to investigate change in outcome achievement over time. To confirm the validity of FOS-R change scores, it must be established that the FOS-R measures the same construct over time; if so, score changes can be attributed to family outcome achievement. However, if not, interpretation of change scores may be misleading. Caregivers (N = 349) of Singaporean children with developmental delays receiving early intervention services completed the FOS-R Part A twice, approximately 1 year apart. Factor analysis was used to confirm the structure of the FOS-R Part A and to assess whether the scale measures the same thing across time (i.e., longitudinal measurement invariance). Results provided support for partial longitudinal measurement invariance, indicating that change scores on this scale can be validly interpreted with certain caveats.